Field
Aspects of the present invention generally relate to a power supply device and an image forming apparatus.
Description of the Related Art
An image forming apparatus adopting an electrophotographic method includes a high-voltage power supply device, which is essential to a process for forming an image on a recording material. As the high-voltage power supply device, for example, one of various modular power supplies such as a charging high-voltage power supply, a developing high-voltage power supply, and a transfer high-voltage power supply is used. These power supplies have different specifications in accordance with the configuration of the image forming apparatus. For example, voltage of an alternating-current high-voltage power supply is superimposed upon voltage of a direct-current high-voltage power supply, or voltage of a direct-current positive high-voltage power supply is superimposed upon voltage of a direct-current negative high-voltage power supply. In addition, various specifications are also possible in terms of specified voltage, specified current, a constant current control method, a constant voltage control method, single-valued output, multi-level value control output, load conditions, and the like.
For example, in the case of transfer voltage, the resistance of a transfer member is measured and the transfer voltage is appropriately controlled in accordance with a result of the measurement, in order to apply, to the transfer member, current necessary to transfer an image. One of various methods for appropriately controlling transfer voltage is an automatic transfer voltage control (ATVC) method disclosed in Japanese Patent Laid-Open No. 11-95581. In the ATVC method, constant voltage control or constant current control is performed on the transfer member using a predetermined value (hereinafter referred to as a “target value”) in a non-image region or between recording sheets, and current or voltage applied to the transfer member at this time is detected. Voltage applied to the transfer member when an image is formed is then controlled based on a result obtained by arithmetically processing the detected voltage or current. Even if the control adopting the ATVC method causes a change in the characteristics of the transfer member due to a change in a surrounding environment of the transfer member or another factor, appropriate current for transferring a toner image can be supplied.
On the other hand, in an operation for cleaning the image forming apparatus, voltage having a polarity opposite that of voltage usually used needs to be applied. For example, in Japanese Patent Publication No. 2-16659, an image forming apparatus is proposed in which voltage having a polarity opposite that of voltage used for transfer is applied to a transfer member and toner left on a surface of a transfer roller is transferred onto an image bearing member using static electricity, in order to remove toner left on the transfer member. In addition, for example, in Japanese Patent Laid-Open No. 2013-78252, voltage having a polarity opposite that of voltage usually used is applied to a secondary transfer roller and a belt cleaning member during a cleaning operation in a configuration including an intermediate transfer member. In this example of the related art, an image forming apparatus is proposed in which toner is prevented from being left on a transfer member and toner that has not been transferred onto a recording material and left on the intermediate transfer member is transferred onto a photosensitive drum and collected.
In addition, in order to separate a recording material from an image bearing member, a transfer roller, or an intermediate transfer member, for example, an electricity eliminating device such as neutralizing pins might be provided. For example, in Japanese Patent Laid-Open No. 2002-372874, an image forming apparatus is proposed in which an electricity eliminating device including a corona discharge unit is provided downstream in a conveying direction of a recording material, and charged particles generated through corona discharge are emitted onto the recording material immediately after the recording material is discharged from a transfer unit.
Currently, further reductions in the size and costs of the image forming apparatus are desired. A high-voltage power supply device included in an image forming apparatus in an example of the related art, an independent high-voltage power supply is provided for each voltage to be applied, such as charging voltage, developing voltage, transfer voltage, or neutralizing voltage. As a result of provision of a large number of components, costs and the area of a circuit board increase. Therefore, the size and costs of the high-voltage power supply device need to be reduced. On the other hand, if a plurality of high-voltage power supplies are integrated with one another, current needs to be accurately detected, in order to make appropriate current flow when an image is formed.